Summary - One year investigation have been carried out in order to determine qualitative and quantitative composition of ichtyopopulations in the lower stream of the river Gvozanka for two seasons: spring-summer and autumn-winter. Fishing was carried out using standard fishing tools, and further investigations of fixed material were carried out in the laboratory of the Center of Ichtyology and Fishery at the Faculty of Science of the University of Sarajevo. During ichtyological investigations in this basin 3 fish species from three families were found. The family Salmonidae is represented with autohtonous brown trout ­ Salmo trutta m. fario (Linnaeus, 1758) and family Thymallidae with grayling ­ Thymallus thymallus (Linnaeus, 1758). From the family Cobitidae, spined loach ­ Cobitis taenia (Linnaeus, 1758) was registered. Total catch during the investigations was 101 specimens or 5.545,51g of ichtyomass. In springsummer period, 57 specimens were catched. The ichtyomass of this sample was 3.441,75g. In the season autumn-winter, 44 specimens were catched. Ichtyomass of this sample was 2.133,76g. The results of investigations of abundance of specimens of certain species in total sample have shown that the most abundant species is brown trout with 53 specimens, followed by spined loach with 43 recorded specimens. The grayling had the lowest abundance with only 5 specimens. The highest recorded ichtyomass was of brown trout with 4.178,80g or 75,35% and the lowest value had grayling with 599,00g or 10,80% of total ichtyomass. The following basic body parameters were analysed: total body lenght, body lenght to the basis of tail fin and body mass. Recorded data of basic body measures of identified species generally fit the findings published elsewhere in literature. Age and sexual structure of the brown trout and grayling specimens in this basin were analysed. These analyses have included 53 specimens of brown trout and specimens of grayling. Analysed specimens of brown trout belonged to the age classes 0+, 1+, 2+, 3+, i 4+. The greatest abundance were registered in age class 1+ (22 specimens or 41,50%) and 2+ (18 specimens or 33,40%). The lowest abundance was present in age class 0+ (only two specimens or 3,80%). The results of the analyses have shown rather greater number of male (67,90%) than female specimens (32,10%) of brown trout in ratio 36:17. Investigated specimens of grayling had belonged to the age classes 1+ i 2+. The greatest abundance was registered in age class 2+ (for specimens or 80,00%) and the lowest abudance in age class 1+ (one specimen or 20,00%). Sexual distribution of grayling is characterised by the highest presence of males (80,00%) in comparison to females (20,00%) in ratio 4:1. Key words: fish populations, Gvozanka river Kratak sadrzaj ­ U cilju utvrivanja kvalitativno-kvantitativnog sastava ihtiofaune donjeg toka rijeke Gvozanke sprovedena su jednogodisnja dvokratna istrazivanja u sezonama; proljee-ljeto i jesenzima. Izlovljavanje riba je obavljeno standardnim ribolovnim alatom, a dalja ispitivanja fiksiranog materijala su obavljena u laboratoriju Centra za ihtiologiju i ribarstvo Prirodno-matematickog fakulteta u Sarajevu. Ihtioloskim istrazivanjima ovog podrucja konstatovane su tri vrste riba iz tri porodice. Porodica Salmonidae je zastupljena potocnom pastrmkom ­ Salmo trutta m. fario Linnaeus, 1758., a porodica

Summary ­ Field research of the upper Krivaja was conducted in October 2004 in order to determine the actual situation of ichthyo-population in the studied running waters. Ichthyo-material was collected, by the representative sampling, from four localities of the upper Krivaja, two localities of its merging rivers ­ Biostice and Stupcanice and one locality of smaller rivers ­ Ocevice, Orlje and Velike Maoce. Ichthyofauna of Biostica is represented with seven species from four families. Salmonidae are represented with brown trout - Salmo trutta m. fario (L.), Thymallidae with grayling - Thymallus thymallus (L.), Cyprinidae with Barbus meridionalis petenyi Heckel, sneep - Chondostoma nasus (L.), chub Leuciscus cephalus (L.) and Phoxinus phoxinus L., and Cottidae bullhead - Cottus gobio L. Out of total number of caught various types of fish, the largest number of the individuals was recorded in the population of brown trout that is represented with 40.86% in the ichthyo-populations of Biostica. Ichthyopopulations of Stupcanica conists of four species from three families. Brown trout - Salmo trutta m. fario (L.) is representative of the family Salmonidae, bullhead - Cottus gobio L. Cottidae, and Barbus meridionalis petenyi Heckel and Alburnoides bipunctatus (Bloch) Cyprinide. Populations of brown trout and Alburnoides bipunctatus (Bloch) Cyprinide with 41.56% and 40.26% shares respectively are the most represented in ichthyofauna of Stupcanica. Six species from four families, Salmonidae, Thymallidae, Cyprinidae and Cottidae represent ichthyofauna of the upper Krivaja. Cyprinids are the most represented with three species / Barbus meridionalis petenyi Heckel, Alburnoides bipunctatus (Bloch) and Chondrostoma nasus (L.)/, while only one representative of the other three families respectively was recorded that is, brown trout - Salmo trutta m. fario (L.), sneep - Thymallus thymallus (L.) and bullhead - Cottus gobio L. The largest number of caught fish was in the population of Alburnoides bipunctatus (Bloch) Cyprinide which is 62.76% in the relative indicators and the smallest number of fish was caught in the population of sneep ­ 1.53%. Five species from four families represent ichthyofauna of river Ocevica. Cyprinidae are represented by two representatives, chub - Leuciscus cephalus (L.) and Alburnoides bipunctatus (Bloch). Brown trout - Salmo trutta m. fario (L.) is representative of the family Salmonidae, sneep is representative of - Thymallus thymallus (L.) Thymallidae and bullhead is from - Coittus gobio L. Cottidae family. Brown trout is the population with the largest number of the caught individuals in Ocevica: 25 or 65,79%. Ichthyofauna of river Orlje consists of two species: brown trout - Salmo trutta m. fario (L.) (family Salmonidae) and bullhead - Cottus gobio L. (Cottidae). Brown trout is dominant species in number with 96.55% share. River Velika Maoca is populated with four fish species. From family Salmonidae evidentirana, brown trout - Salmo trutta m. fario (L.) was recorded, Cyprinidae chub - Leuciscus cephalus (L.), Barbus meridionalis petenyi Heckel and Alburnoides bipunctatus (Bloch). The population of Alburnoides bipunctatus is the most represented species by number, with 64,18%.